There is a need for composite panels, particularly in the building industry, wherein rigid outer skins, for example rolled steel sheet, are laminated with a rigid foam core. Various apparatus are known to continuously make such composite panels, but the use of rigid outer skins presents many production problems.
A foam probe that extends between the outer skins into the molding zone to lay down a pattern of foamable chemicals has a disadvantage that there is a large pressure drop in such a probe that would of necessity be as long as the width of the panels, which may be three or more feet in width. The foamable chemicals are mixed prior to their travel into and through the probe, so that they are mixed completely outside of the molding zone and must travel for three or more feet within the probe, during which time they are starting to react. It is desirable to have the reaction time as fast as possible so that the length of the pressure and curing tunnel may be as short as possible and the speed of the production line may be as fast as possible. However, it is also desirable to have the reaction time as slow as possible with respect to such a long probe, because if the foam were to react fast it would be exerting considerable back pressure in the probe as it expands in the probe and further it would tend to permanently deposit in and clog up the probe. Further if separate panels are being made on a continuous basis, withdraw of the probe from one panel would result in the mixed foamable chemicals remaining static within the long probe until the next panel comes into position, which combined with the length of the probe compounds the above problems.
It is known to connect the opposite edges of the panel skins with separate connectors to form a hinge, and to pivot the skins about their back edge for an angle of 45.degree. or more in order to insert bulky foam depositing apparatus, but this in turn is not a satisfactory solution, because considerable room would thereafter be necessary to pivot the skins back into their final parallel position before they could enter into a pressure and curing tunnel, which again would require a very slow reacting speed for the foamable chemicals so that the skins could be reassembled in their final parallel relationship and enter the pressure and curing tunnel before substantial expansion; this would correspondingly either greatly slow down the process or greatly increase the length of the pressure and curing tunnel.
The construction of the pressure and curing tunnel must be very rigid to resist the substantial foaming pressures, which may be in the order of 5 pounds per square inch, and further to form rigid backing so that an accurate product may be formed. Thus, the expense per linear foot of the pressure and curing tunnel is considerably high so that it is advantageous to construct it as short as possible. At the same time, it is of course advantageous to construct the entire apparatus such that the linear speed of the product may be as high as possible to gain the most production from a single line.